Most of the whole blood collected from donors today is not itself stored and used for transfusion. Instead, the whole blood is separated into its clinically proven components (typically red blood cells, platelets, and plasma), which are themselves individually stored and used to treat a multiplicity of specific conditions and diseased states. For example, the red blood cell component is used to treat anemia; the concentrated platelet component is used to control thrombocytopenic bleeding; and the platelet-poor plasma component is used as a volume expander or as a source of Clotting Factor VIII for the treatment of hemophilia.
During centrifugal blood processing, an interface develops between the red blood cell and plasma components. Leukocytes occupy this interface, which is also referred to as the buffy coat.
In collecting whole blood components for transfusion, it is desirable to minimize the presence of impurities or other materials that may cause undesired side effects in the recipient. For example, because of possible febrile reactions, it is generally considered desirable to transfuse red blood cells and plasma substantially free of leukocytes, particularly for recipients who undergo frequent transfusions.
It is therefore important during blood processing to be able to accurately identify the leukocyte-rich interface between red blood cell and plasma components, so that processing can be controlled to isolate the interface from the other components. This need exists not only for automated blood collection procedures, but also for manual blood collection procedures.
Conventional systems and methods often employ optical signal processing to identify and control the interface. Such systems often have limited tolerance to "noise", which leads to false readings. Such noise can arise due to variations in the performance of the optical elements, especially when multiple optical elements are used in tandem, since optical elements are known to have a high degree of variability in gain, focus, and directivity. Mechanical vibration is another source of noise.
Blood components are "sticky" and can smear along the sides of a separation chamber or bag. The smearing is yet another category of noise, as it leads to false readings and the incorrect identification of the interface.